350 valve covers leaking and leaking and leaking - Hot Rod Forum : Hotrodders Bulletin Board
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Old 10-18-2012, 08:35 AM
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350 valve covers leaking and leaking and leaking

I have an early small block 350 that for the life of me I can't get the valve covers to stop leaking. I tried the cork and rubber gaskets and now I'm going to try using a rubber gasket with the steel core. The valve covers themselves are stamped and the heads have studs in them for holding the covers down. I've cleaned the surfaces on the head and valve cover a few different times, tried everything from tightening the nuts down from 45 inlb to 5 lbft. I know the heads aren't bad cuz they weren't leaking before I decided to take the valve covers off the engine a little while ago. Any suggestions on what else I should try? Should I be using a specific pattern for tightening the nuts on the studs?

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Old 10-18-2012, 12:05 PM
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350 valve covers leaking and leaking and leaking

Try again with the cork gaskets and clean everything with some acetone. Use some Indian Head compound on both the valve cover and the valve cover rail. Don't over-tighten the fasteners just snug them using a 1/4 drive ratchet and socket.
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Old 10-18-2012, 12:50 PM
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I agree with the above post this stuff has NEVER failed me. Use it to glue the gasket to the valve cover then apply another layer onto the head and gasket and install the valve cover. It should stick in place and keep everything from moving while you instll the bolts. Also should help keep the gasket in place while you get the cover bolted down.

Dont over tighten the bolts. Let the sealer setup before you snug everything down. Then only tight enough to keep them from backing off.

If it still leaks get new valve cover they are bent. If steel cover with pushed out bolt holes. Use a small socket and a hammer to bend them back the other way. Just be gentle. Several small taps will get it back in line.

This stuff always works. The best for water pumps as well.
Permatex 20539 Indian Head Gasket Shellac Compound

Hope this helps.
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Old 10-18-2012, 12:54 PM
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#1 - Make sure the covers are flat around the mounting holes, they distort over time or if overtightened.

#2 - Use spreader bars to distribute the clamping load over more area of the gasket rail. On SBC's I use them with studs and stainless steel lock nuts.

#3 - Use the steel core rubber gaskets.

I had a 350 Chevy and a 318 Dodge both with leaky steel covers, I did the 3 things above in conjunction with each other and no more leaks.
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Old 10-18-2012, 01:00 PM
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Quote:
Originally Posted by 85cjsm350 View Post
I have an early small block 350 that for the life of me I can't get the valve covers to stop leaking. I tried the cork and rubber gaskets and now I'm going to try using a rubber gasket with the steel core. The valve covers themselves are stamped and the heads have studs in them for holding the covers down. I've cleaned the surfaces on the head and valve cover a few different times, tried everything from tightening the nuts down from 45 inlb to 5 lbft. I know the heads aren't bad cuz they weren't leaking before I decided to take the valve covers off the engine a little while ago. Any suggestions on what else I should try? Should I be using a specific pattern for tightening the nuts on the studs?
Some of these old heads with the as cast gasket rail just can't be stopped because the mating surface is too uneven, rough, sometimes narrows.

The other problem is that with use and age the cover forms dimples around the hold down holes and the cover overall develops twists along the gasket rail that prevent it from evenly loading the gasket. The dimples can be worked out with a small ball peen hammer over a socket or small diameter pipe such that you can flatten them if not pooch the materail up around the hole, just a little bit. The other big thing that will help at this point are hold down tabs that spread the load over more area, <<< 1955-1961, 1968-1981 Chevrolet Corvette Valve Cover Hold Down Tab Set - Engine Mechanical - Edelbrock 55-61, 68-81 Corvette Valve Cover Hold Down Tab Set - 14067-03133273 - PartsGeek >>> You'll need two sets.

These things have a groove and ridge near the outboard side, for the first time I use them I'd put them on groove down to the cover and ridge up to see if they work without maring the gasket rail. If not turn them over.

Bogie
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Old 10-19-2012, 08:44 PM
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covers leaking?

i always put weather strip adhesive on cover then use thread through holes to hold the cork gasket in place,turn them upside down with a heavy book on them till morning, then smear a slight film of silicone on the head side and install useing spreader bars,next time you take them off rub the thin film off with your finger and reapply film and good to go again,you can do this 3-4 times before replacing gasket!!!i do this all the time to adjust solid lifters ... i hate leaks!!!!!!!
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Old 10-19-2012, 09:07 PM
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personally i would get rid of the cheap stamped valve covers and get a good pair of valve covers made from a thicker material. and use the rubber gasket gasket with a steele core . also permatex right stuff is a good gasket maker
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Old 04-17-2016, 08:39 AM
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Valve cover leaks

I have the same problem with a set of finned (Cast) Valve covers, no matter which gasket I use or what sealer I put on. The Covers are flat and clean, the heads are too. 50 years working on cars and I never had a problem like this!
It's only on the left side, I can feel the film at the bottom of the valve cover (Over the header) where it bolts to the head... After it's been run 15 minutes or more.
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Old 04-17-2016, 11:13 AM
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I have never had SB Chevrolet 327 style valve covers or Corvette finned cast aluminum valve covers leak. I put breathers in the sides of the SB Corvette aluminum valve covers but never noticed any difference.

I seal and stick the cork gaskets to the 327 style stamped valve covers with black gasket adhesive, align the holes in the valve covers with the holes in the gaskets while the sealer is still tacky, then let the covers sit for 30 minutes before installing them. I use the steel spreader tabs under the heads of the valve cover screws just like the factory did. I used that procedure with solid lifters on a 30-30 cam that required valve lash adjustment occasionally. The 327 style stamped steel valve covers do not have breathers and the 327 engines I had and have now only had a road draft tube and did not have a PCV. The only breather on the engine is the push on breather on front oil fill tube. However, I never did any and don't do any long sustained high speed driving on the highways. Never had any leaks...just lucky I guess

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Old 04-17-2016, 11:29 AM
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Valve cover leaks, continued...

I tried all that is mentioned here... Nope "Didn't work!"
The only other thing I can think of is that the Valve covers are porous and the oil is seeping through!
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Old 04-17-2016, 11:41 AM
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I don't understand this problem. Valve cover leaking is a oil leak I have never had with a SB Chevrolet engine. I have never had a Chevrolet engine with center bolt valve covers, except on my 1991 S10 Blazer 4.3L engine. No leaks with that one either. I don't use any more sealer than is necessary to stick the cork gaskets to the valve covers. The cork gaskets conform to the irregular gasket rails on the cast iron heads. Let the gasket do the sealing. Don't put any sealer on the engine or on the heads.
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Old 04-17-2016, 04:22 PM
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That was the first thing I did, put them on dry... Leaked!
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Old 04-17-2016, 04:31 PM
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I clean the seal surfaces completely... lay valve covers edges on a straight hunk of metal and tap them flat... use RTV/DAP blacksilicone rubber sealant to put them on... don't really tighten the bolts, just snug them enough to keep the valve covers from falling off... let the RTV do the sealing job... give the RTV a couple hours or more to cure before running engine... If doing a race engine and need to run it quickly, will need a different technique...
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Old 04-17-2016, 04:31 PM
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Quote:
Originally Posted by bigalturk1 View Post
That was the first thing I did, put them on dry... Leaked!
You tried the gasket shellac in post 3 that stuff always works did you let it dry a bit before sticking them down then let it set over night should stick the covers to the heads without any issues. Cheap cork gaskets should do the trick. Certainly never had it fail the same day after letting it dry only thing that will make it fail is getting oil on the gaskets prior to sticking them in place.

I would try it again with the Indian head stuff it will work. If not its the covers are not flat. Setting them on a glass table will show you any none flat areas with a feeler gauge. Over tighten them can cause the issue but normally unless they are really bent the shellac will hold them down fast. Maybe let it set over night.

Hope this helps.
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Old 04-17-2016, 04:33 PM
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Quote:
Originally Posted by BuzzLOL View Post
I clean the seal surfaces completely... lay valve covers edges on a straight hunk of metal and tap them flat... use RTV/DAP blacksilicone rubber sealant to put them on... don't really tighten the bolts, just snug them enough to keep the valve covers from falling off... let the RTV do the sealing job... give the RTV a couple hours or more to cure before running engine... If doing a race engine and need to run it quickly, will need a different technique...
RTV will leak on valve cover cork gaskets. Better to run them dry than with rtv. Rubber gaskets should also seal dry with flat covers.
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